Feedback Control System and Method

ABSTRACT

The present disclosure provides a feedback control system and method for a bidirectional VCM. The system employs an analog core that is common to both the PWM and linear modes of operation. The analog core includes a feedback mechanism that determines the error in the current flowing through the motor. The feedback mechanism produces an error voltage that corresponds to the current error, and applies the voltage to a control driver. The control driver then controls the motor, based on the error voltage, in either a PWM or linear mode. By sharing a common core, the switching time between modes is improved. Furthermore, the output current error between modes is reduced.

PRIORITY DATA

This application is a non-provisional of U.S. Provisional PatentApplication Ser. No. 62/164,873, filed May 21, 2015, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a feedback control system and method.In particular, the present disclosure relates to a feedback controlsystem and method for use with a voice coil motor.

BACKGROUND

Voice coil motors (VCMs) are actuators used to drive electromagneticloads. Applications typically use VCMs due to their small size, lowcost, and shock resistance. Moreover, VCM applications frequentlyrequire both forward and reverse VCM operations. For example, VCMs areused to move the read/write head in hard disk drive applications and areused to focus lenses in imaging applications.

Generally, VCMs include at least a permanent magnetic circuit and acoil. In a closed loop feedback system, a VCM interacts with a bridgecircuit that drives a current through an electromagnetic load of theVCM.

To drive the current, a first set of analog circuitry that provides adynamic, or linear, driving operation is often used in conjunction withthe VCM. Dynamic drivers provide reliably linear drive signals to theelectromagnetic load. However, dynamic drivers are inefficient as theydissipate a relatively large amount of power. Designers generally usedynamic drivers only in circumstances in which it is important tominimize noise and in which electromagnetic compatibility (EMC) iscritical.

As an alternative to drive the current, a second set of circuitry thatprovides a pulse width modulation (PWM) driving operation is used inconjunction with the VCM. PWM drivers are more efficient and dissipaterelatively less power than dynamic drivers. However, PWM driversgenerate a great deal of radiative and conductive noise that caninterfere with sensitive circuit operations proximate or connected tothe VCM.

Previous VCM driving schemes generally provide systems that use only thedynamic driving operation or the PWM driving operation. In somecircumstances in which both the dynamic and the PWM driving operationsare used with respect to the same motor, it is often the case that themotor cannot also be operated in both a forward direction and a reversedirection for each of the dynamic and the PWM driving operations.

In some other circumstances in which both the dynamic and the PWMdriving operations are performed with respect to the same motor, eachdriving operation is associated with a different set of core analogcomponents in the feedback loop. Switching between the different sets ofcore analog components requires a transition period of time between theimplementation of the different modes. Additionally, switching betweenthe different sets of core analog components introduces an outputcurrent error between modes.

Accordingly, there exists a need for an improved voice coil motor driverthat is capable of driving a load using both a PWM mode and a linearmode.

SUMMARY

The present disclosure provides a feedback control system and method fora VCM. The system utilises an analog core that is common to both the PWMand linear modes of operation. The analog core includes a feedbackmechanism that determines the error in the current flowing through themotor. The feedback mechanism produces an error voltage that correspondsto the current error, and applies the voltage to a control driver. Thecontrol driver then controls the motor, based on the error voltage, ineither a PWM or linear mode. By sharing a common core, the switchingtime between modes is improved. Furthermore, the output current errorbetween modes is reduced.

In a first aspect, the present disclosure provides a feedback controlsystem, comprising: an analog core; a control driver; and anelectromagnetic load of a voice coil motor (VCM); wherein the analogcore is arranged provide feedback from the electromagnetic load to thecontrol driver in order to regulate the current consumption of the VCM;the control driver is arranged to receive, from the analog core, anerror voltage corresponding to an error in the current being driven ontothe electromagnetic load; and the control driver is further arranged tocontrol the current driven onto the electromagnetic load based on theerror voltage.

The feedback control system may operate in a closed loop. The controldriver may interchangeably operate in a linear mode (sometimes called adynamic mode) and a pulse width modulation (PWM) mode. The controldriver, in each of the linear mode and the PWM mode, may furtherinterchangeably operate the motor in a forward direction and a reversedirection. During operation in each of the linear mode and the PWM mode,the analog core may be used to bi-directionally drive the motor. Theinterchangeability of the analog core results in low DC voltage errorbetween the operation of the motor in the linear mode and the PWM mode.

The analog core of the feedback control system may include at least: acollection of NMOS switches (n-type MOSFETs) and PMOS switches (p-typeMOSFETs) and an operational amplifier. In some embodiments, the analogcore may further include at least one of: a resistive digital-to-analogconverter (r-DAC), voltage switches, and a resistor. The collection ofNMOS switches and PMOS switches within the analog core may be generallyin the formation of an H-bridge circuit.

In a second aspect, the present disclosure provides a controller for avoice coil motor (VCM) in which the controller is arranged to operatethe voice coil motor bidirectionally in linear and pulse widthmodulation modes.

In a third aspect, the present disclosure provides a method ofcontrolling the current applied to an electromagnetic load of a voicecoil motor (VCM), comprising: driving an electromagnetic load of a voicecoil motor (VCM); receiving from an analog core, at a control driver, anerror voltage corresponding to an error in the current being driven ontothe electromagnetic load; controlling, using the control driver, thecurrent driven onto the electromagnetic load based on the error voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 shows a feedback control system in accordance with an embodimentof the disclosure;

FIG. 2 shows control driver in accordance with an embodiment of thedisclosure;

FIGS. 3A to 3D show a feedback control system and a control driver beingoperated in a linear mode, in accordance with an embodiment of thedisclosure;

FIGS. 4A to 4D show a feedback control system and a control driver beingoperated in a pulse width modulation mode, in accordance with anembodiment of the disclosure;

FIG. 5 shows a feedback control system in accordance with an embodimentof the disclosure;

FIG. 6 shows a feedback control system in accordance with an embodimentof the disclosure;

FIG. 7 shows a feedback control system in accordance with an embodimentof the disclosure;

FIGS. 8A to 8D show a feedback control system and a control driver beingoperated in a pulse width modulation and a linear mode, in accordancewith an embodiment of the disclosure;

FIG. 9 is a chart showing the effect of offset error on a VCM transferfunction; and

FIG. 10 is a chart showing the effect of gain error on a VCM transferfunction.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure provides a feedback control system for abidirectional VCM. The feedback control system includes an analog coreand a control driver. The analog core determines an error in the currentflowing in the motor, and generates an error voltage. The error voltageis used by the control driver to drive the motor. The control driver isarranged to drive the motor in PWM and linear modes. The analog core isused in both modes. Because the same analog core is used in both modes,switching times between modes are improved. Furthermore, output currenterror between modes is reduced. The control driver is also arranged todrive the motor in forwards and reverse directions in both PWM andlinear modes.

FIG. 1 depicts an embodiment of a feedback control system 100 providinga bi-directional driver having a PWM mode and a linear mode. Thefeedback control system can include:

-   -   an operational amplifier 102;    -   a PWM/linear control driver 104;    -   a set of MOSFET switches (106, 108, 110, 112, 114, and 116);    -   a motor 118; and    -   sensing circuitry 120.

Typically the set of MOSFET switches includes three groups of switches.

A first group of MOSFET switches (e.g., 106 and 108) accepts a voltagefrom the PWM/linear control driver 104 and regulates the output current.At any given time, only one of the switches from the first group ofMOSFET switches is ON and regulating the output current while the otherswitches in the first group are OFF, or disabled. As shown in FIG. 1,the switches in the first group of MOSFET switches are configured to bep-type MOSFETs. The first group of switches operates during both the PWMmode and the linear mode.

A second group of MOSFET switches (e.g., 110 and 112) are switches forrecirculation of the current. At most, only one of the switches from thesecond group of MOSFET switches is ON and recirculating the current. Aswitch from the second group of MOSFETs is activated, or turned ON, onlyin the PWM mode. During the linear mode, all of the switches in thesecond group are OFF. As shown in FIG. 1, the switches in the secondgroup of MOSFET switches are configured to be n-type MOSFETs.

A third group of MOSFET switches (e.g., 114 and 116) are switches thatsteer the current in one direction or another direction. This group ofswitches controls the motor being actuated in a forward direction or areverse direction. At any given time, only one of the switches from thethird group of MOSFET switches is ON and steering the current. The thirdgroup of switches operates during both the PWM mode and the linear mode.As shown in FIG. 1, the switches in the third group of MOSFET switchesare configured to be n-type MOSFETs.

During a linear mode, the voltage output from the PWM/linear controldriver 104 is applied directly to one switch from the first group ofMOSFET switches. The MOSFET switch that is ON operates as a currentsource and begins regulating the current supplied to the motor 118. Inan operation during linear mode, the current flows: from the selectedMOSFET from the first group of MOSFET switches, which acts as currentsource (either 106 or 108); through the motor 118; and through theselected MOSFET from the third group of MOSFET switches, whichdetermines the direction of the motor (either 114 or 116).

During a PWM mode, the voltage output from the PWM/linear control driver104 is applied to one switch from the first group of MOSFET switchesthat works in combination with one of the switches from the second groupof MOSFET switches. The combination of switches from the first group andthe second group (e.g., 106 and 110 or 108 and 112) operate as aninverter. Accordingly, the current applied to the motor 118 during thePWM mode is pulsed as either fully ON or fully OFF. In an operationduring PWM mode, the current flows in pulses regulated by thecombination of the switches from the first group of MOSFET switches andthe second group of MOSFET switches: from the selected MOSTFET from thefirst group of MOSFET switches (either 106 or 108); through the motor118; and through the selected MOSFET from the third group of MOSFETswitches, which determines the direction of the motor (either 114 or116).

Sensing circuitry 120 provides a circuit component that translates thecurrent available at the junction above 120, which represents the amountof current flowing through the motor 118, into a feedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 102 for feedback purposes. Theoperational amplifier 102 compares the feedback voltage at the negativeterminal to a reference voltage at the positive terminal and generates avoltage representative of the difference, or error, between thereference voltage and the feedback voltage. The error is then used byPWM/linear control driver 104 to drive the motor accordingly.

In some example embodiments, the first group of MOSFET switches isconfigured to include n-type MOSFETs and the third group of MOSFETswitches is configured to include p-type MOSFET switches. In such anarrangement, the sensing circuitry is instead provided at the top of thecircuit and has a junction proximate to the first group of MOSFETswitches.

FIG. 2 depicts an embodiment of a bi-directional PWM/linear controldriver 200 having a PWM mode and a linear mode. The PWM/linear controldriver can include:

-   -   buffers 204, 206, and 208;    -   a ramp signal 210;    -   an operational amplifier 212;    -   a PWM digital controller 214;    -   a direction logic 230; and    -   a not gate (or inverter) 232.

On the input side, the PWM/linear control driver 200 accepts at leastthree signals including: an analog signal 202; a motor directionalitysignal 228; and a control mode signal 240. The analog signal is theerror signal generated by the operational amplifier 102 in the feedbackcontrol system 100. The motor directionality signal 228 can be either ananalog signal or a digital signal and is used to select whether themotor operates in the forward direction or the reverse direction. Thecontrol mode signal 240 can be either an analog signal or a digitalsignal and is used to select whether the motor operates in the PWM modeor the linear mode.

On the output side, the PWM/linear control driver 200 generates at leastthree sets of signals. The first set of PWM/linear control driver outputsignals, 220, corresponds to those signals used to control the firstgroup of MOSFET switches. The first set of output signals 220 includessignal 216 and signal 218, which each control a different switch (e.g.,216 controls switch 106 and 218 controls switch 108). The second set ofPWM/linear control driver output signals, 226, corresponds to thosesignals used to control the second group of MOSFET switches. The secondset of output signals, 226, includes signal 222 and 224, which eachcontrol a different switch (e.g., 222 controls switch 110 and 224controls switch 112). The third set of PWM/linear control driver outputsignals, 238, corresponds to those signals used to control the thirdgroup of MOSFET switches. The third set of output signals 238 includessignal 234 and 236, which each control a different switch (e.g., 238controls switch 114 and 236 controls switch 116).

Analog signal 202 is applied to the PWM/linear control driver 200 andpasses through buffers 204, 206, and 208. Buffers 204, 206, and 208 canbe clocked and synchronized with one another. The voltage signal exitingbuffer 208 is applied to the negative terminal of operational amplifier212. A ramp signal, or a saw-tooth signal 210, is applied to thepositive terminal of the operational amplifier 212. The output ofoperational amplifier is dependent upon the level of the voltagesupplied at the negative input terminal, and the output is a squarewave. The square wave output is supplied to the PWM digital controller214. PWM digital controller 214 further accepts as an input the controlmode signal 240.

If the control mode signal 240 indicates that the control mode is alinear mode (e.g. control mode signal 240 is a 1), then the PWM digitalcontroller 214 deactivates signals 222 and 224. Also in the linear mode,PWM digital controller 214 acts as a control signal and allows for theoutput from one of buffers 204 and 206 to directly and continuously flowto the appropriate switch from the first group of MOSFET switches.

If the control mode signal 240 indicates that the control mode is a PWMmode (e.g. control mode signal 204 is a 0), then the PWM digitalcontroller 214 activates outputs 222 and 224. The square wave generatedfrom the output of the operational amplifier 212 is provided to one of216 and 218 such that the pulsing square wave signal flows to theappropriate switch from the first group of MOSFET switches.Simultaneously, the PWM digital controller 214 provides an invertedversion of the square wave generated from the output of the operationalamplifier 212 to an appropriate one of outputs 222 and 224.

The signal selected from outputs 222 and 224, and thereby the switchfrom the second group of MOSFET switches 110, 112, is selected tocorrespond to the signal from the first group of MOSFET switchesreceiving the square wave. For example, if the square wave is providedalong output 216, which corresponds to switch 106, then the invertedsquare wave is provided along output 222, which corresponds to switch110. If the square wave is provided along output 218, which correspondsto switch 108, then the inverted square wave is provided along output224, which corresponds to switch 112.

The motor directionality signal 228 is at least provided to thedirection logic 230. In some embodiments, the motor directionalitysignal 228 is advantageously further connected to the PWM digitalcontroller 214. According to a selection of a forward operation of themotor or a reverse operation of the motor, the direction logic 230provides an output signal. The output signal from 230 is, along onechannel, inverted by a not gate so that the outputs 234 and 236 arealways inverse values.

In some embodiments, the motor directionality signal is provided basedon a sensed current value of the feedback control system. The sensedcurrent is the same current sensed by 120. When the current value isgreater than zero (Iout>0), direction logic 230 provides an outputsignal that will operate the motor in a forward direction. When thecurrent value is less than zero (Iout<0), direction logic 230 providesan output signal that will operate the motor in a reverse direction.

FIG. 3A depicts an embodiment of a feedback control system 300 includinga bi-directional driver that is operating in a forward direction whilein a linear mode. In a feedback control system 300 for a VCM with abi-directional driver that is operating in a forward direction while ina linear mode, the feedback control system includes:

-   -   an operational amplifier 302;    -   a PWM/linear control driver 304;    -   a set of MOSFET switches (306, 308, 310, 312, 114, and 316);    -   a motor 318; and    -   sensing circuitry 320.

During the linear mode, the voltage output from the PWM/linear controldriver 304 is applied directly to one switch, switch 306, from the firstgroup of MOSFET switches. MOSFET switch 306 operates as a current sourceand begins regulating the current supplied to the motor 318. The currentflows from MOSFET 306, which acts as the current source and through themotor 318. PWM/linear control driver 304 further activates MOSFET 316 sothat the motor rotates in the forward direction. The current exiting themotor 318 flows through switch 316.

Sensing circuitry 320 provides a circuit component that translates thecurrent available at the junction above 320, which represent the amountof current flow through the motor 318, into a feedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 302. The operational amplifier 302compares the feedback voltage at the negative terminal to a referencevoltage at the positive terminal and generates a voltage representativeof the difference, or error, between the reference voltage and thefeedback voltage. The error is then used by PWM/linear control driver304 to drive the motor accordingly.

FIG. 3B depicts a configuration of a bi-directional PWM/linear drivercontrol 304 that is operating in a forward direction while in a linearmode.

For the feedback control system 300, FIG. 3B depicts the signalsprovided as outputs from the PWM/linear control driver 304. As thedriver is in a linear mode, the error signal from operational amplifier302 is buffered and provided directly and continuously through thePWM/linear control, over output 322, to switch 306. To activate only oneswitch from the first group of MOSFETs, output 324 is OFF. Provided thatthe feedback control system is in linear mode, both of the outputsassociated with the second group of MOSFETs are OFF (e.g., 326 and 328).To drive the motor in the forward direction, output 332 is ON, whileoutput 330 is OFF. Output 332 drives the switch 316 from the third groupof MOSFETs.

FIG. 3C depicts an embodiment of a feedback control system 300 includinga bi-directional driver that is operating in a reverse direction whilein a linear mode.

In a feedback control system 300 for a VCM with a bi-directional driverthat is operating in a reverse direction while in a linear mode, thefeedback control system includes:

-   -   an operational amplifier 334;    -   a PWM/linear control driver 336;    -   a set of MOSFET switches (338, 340, 342, 344, 346, and 348);    -   a motor 350; and    -   sensing circuitry 352.

During the linear mode, the voltage output from the PWM/linear controldriver 336 is applied directly to one switch, switch 340, from the firstgroup of MOSFET switches. MOSFET switch 340 operates as a current sourceand begins regulating the current supplied to the motor 350. The currentflows from MOSFET 340, which acts as the current source and through themotor 350. PWM/linear control driver 336 further activates MOSFET 346 sothat the motor rotates in the reverse direction. The current exiting themotor 350 flows through switch 346.

Sensing circuitry 352 provides a circuit component that translates thecurrent available at the junction above 352, which represent the amountof current flow through the motor 350, into a feedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 334. The operational amplifier 334compares the feedback voltage at the negative terminal to a referencevoltage at the positive terminal and generates a voltage representativeof the difference, or error, between the reference voltage and thefeedback voltage. The error is then used by PWM/linear control driver336 to drive the motor accordingly.

FIG. 3D depicts a configuration of a bi-directional PWM/linear controldriver 336 that is operating in a reverse direction while in a linearmode.

For the feedback control system 300, FIG. 3D depicts the signalsprovided as outputs from the PWM/linear control driver 336. As thedriver is in a linear mode, the error signal from operational amplifier334 is buffered and provided directly and continuously through thePWM/linear control driver, over output 356, to switch 340. To activateonly one switch from the first group of MOSFETs, output 354 is OFF.Provided that the feedback control system is in linear mode, both of theoutputs associated with the second group of MOSFETs are OFF (e.g., 358and 360). To drive the motor in the reverse direction, output 362 is ON,while output 364 is OFF. Output 362 drives the switch 346 from the thirdgroup of MOSFETs.

Although the numbering associated with FIGS. 3A, 3B, 3C, and 3D differs,it should be noted that this is for clarification and reference purposesonly. FIGS. 3A and 3C show the same feedback control system and circuitcomponents. FIGS. 3B and 3D show the same PWM/linear control driver thatis in each circumstance configured in a different manner based on inputsignals provided to the PWM/linear control driver.

FIG. 4A depicts an embodiment of a feedback control system 400 includinga bi-directional driver that is operating in a forward direction whilein a PWM mode.

In a feedback control system 400 for a VCM with a bi-directional driverthat is operating in a forward direction while in a PWM mode, thefeedback control system includes:

-   -   an operational amplifier 402;    -   a PWM/linear control driver 404;    -   a set of MOSFET switches (406, 408, 410, 412, 414, and 416);    -   a motor 418; and    -   sensing circuitry 420.

During the PWM mode, the voltage output from the PWM/linear controldriver 404 is applied directly to one switch, switch 406, from the firstgroup of MOSFET switches. The PWM/linear control driver 404 furtheractivates one switch, switch 410, from the second group of MOSFETswitches such that together switches 406 and 410 act as an inverter.Switches 406 and 410 drive the current to flow through the motor 418.PWM/linear control driver 404 further activates MOSFET 416 so that themotor rotates in the forward direction. The current exiting the motor418 flows through switch 416.

Sensing circuitry 420 provides a circuit component that translates thecurrent available at the junction above 420, which represent the amountof current flow through the motor 418, into a feedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 402. The operational amplifier 402compares the feedback voltage at the negative terminal to a referencevoltage at the positive terminal and generates a voltage representativeof the difference, or error, between the reference voltage and thefeedback voltage. The error is then used by PWM/linear control driver404 to drive the motor accordingly.

FIG. 4B depicts a configuration of a bi-directional PWM/linear controldriver 404 that is operating in a forward direction while in a PWM mode.

For the feedback control system 400, FIG. 4B depicts the signalsprovided as outputs from the PWM/linear control driver 404. As thedriver is in a PWM mode, the error signal from operational amplifier 402is buffered and applied to the negative terminal of another operationalamplifier (e.g., operational amplifier 212 in FIG. 2). A ramp signal isapplied to the positive terminal of the operational amplifier. Theoutput of operational amplifier, which is a square wave, is supplied toa PWM digital controller. The PWM digital controller applies the output,via 422, to switch 406. To activate only one switch from the first groupof MOSFETs, output 424 is OFF. Provided that the feedback control systemis in PWM mode, the inverse of the square wave is driven onto output 426to drive switch 410 from the second group of MOSFETs.

To drive the motor in the forward direction, output 432 is ON, whileoutput 430 is OFF. Output 432 drives the switch 416 from the third groupof MOSFETs.

FIG. 4C depicts an embodiment of a feedback control system 400 includinga bi-directional driver that is operating in a reverse direction whilein a PWM mode.

In a feedback control system 400 for a VCM with a bi-directional driverthat is operating in a reverse direction while in a PWM mode, thefeedback control system includes:

-   -   an operational amplifier 434;    -   a PWM/linear control driver 436;    -   a set of MOSFET switches (438, 440, 442, 444, 446, and 448);    -   a motor 450; and    -   sensing circuitry 452.

During the PWM mode, the voltage output from the PWM/linear controldriver 436 is applied directly to one switch, switch 440, from the firstgroup of MOSFET switches. The PWM/linear control driver 436 furtheractivates one switch, switch 444, from the second group of MOSFETswitches such that together switches 440 and 444 act as an inverter.Switches 440 and 444 drive the current to flow through the motor 450.PWM/linear control driver 436 further activates MOSFET 446 so that themotor rotates in the reverse direction. The current exiting the motor450 flows through switch 446.

Sensing circuitry 452 provides a circuit component that translates thecurrent available at the junction above 452, which represent the amountof current flow through the motor 450, into a feedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 434. The operational amplifier 434compares the feedback voltage at the negative terminal to a referencevoltage at the positive terminal and generates a voltage representativeof the difference, or error, between the reference voltage and thefeedback voltage. The error is then used by PWM/linear control driver436 to drive the motor accordingly.

FIG. 4D depicts a configuration of a bi-directional PWM/linear controldriver 436 that is operating in a reverse direction while in a PWM mode.

For the feedback control system 400, FIG. 4D depicts the signalsprovided as outputs from the PWM/linear control driver 434. As thedriver is in a PWM mode, the error signal from operational amplifier 434is buffered and applied to the negative terminal of another operationalamplifier (e.g., operational amplifier 212 in FIG. 2). A ramp signal isapplied to the positive terminal of the operational amplifier. Theoutput of operational amplifier, which is a square wave, is supplied toa PWM digital controller. The PWM digital controller applies the output,via 456, to switch 440. To activate only one switch from the first groupof MOSFETs, output 454 is OFF. Provided that the feedback control systemis in PWM mode, the inverse of the square wave is driven onto output 460to drive switch 444 from the second group of MOSFETs.

To drive the motor in the reverse direction, output 462 is ON, whileoutput 464 is OFF. Output 562 drives the switch 446 from the third groupof MOSFETs.

Although the numbering associated with FIGS. 4A, 4B, 4C, and 4D differs,it should be noted that this is for clarification and reference purposesonly. FIGS. 4A and 4C show the same feedback control system and circuitcomponents. FIGS. 4B and 4D show the same PWM/linear control driver thatis in each circumstance configured in a different manner based on inputsignals provided to the PWM/linear control.

Similarly, although the numbering associated with FIGS. 3A, 3B, 3B, and3D differs from the numbering associated with FIGS. 4A, 4B, 4C, and 4D,it should again be noted that this is for clarification and referencepurposes only. FIGS. 3A, 3C, 4A, and 4C show the same feedback controlsystem and circuit components. FIGS. 3B, 3D, 4B, and 4D show the samePWM/linear control driver that is in each circumstance configured in adifferent manner. FIG. 3 overall shows the feedback control system andPWM/linear control configurations for a bidirectional driver while it isoperating in a linear mode. FIG. 4 overall shows the same feedbackcontrol system and PWM/linear control configurations for the samebidirectional driver while it is operating in a PWM mode.

FIG. 5 depicts a feedback control system having an analog core 500 and abi-directional control driver 504 having a PWM mode and a linear mode.

Analog core 500 includes analog circuit components in place of thesensing circuitry described in foregoing FIGS. 1 to 4. Analog core 500capitalizes on the reuse of the sensing circuitry to reduce DC errorbetween the linear mode and the PWM mode. Analog core 500 can include:

-   -   an operational amplifier 502;    -   a resistive digital-to-analog converter (r-DAC) 522;    -   a set of MOSFET switches (506, 508, 510, 512, 514, and 516); and    -   sensing circuitry.

Sensing circuitry is, in analog core 500, a sensing resistor 520 and anr-DAC (or digital potentiometer) 522. In some embodiments, the r-DACincludes a resistor ladder integrated circuit. In other embodiments, ther-DAC includes a digital-to-analog converter. r-DAC 522 accepts, as aninput, a digital code.

The digital code provides a number of bits as an instruction to ther-DAC 522. The number of bits characterizes, as the instruction, thedegree to which resistance should be varied in the r-DAC. For example,an 8-bit digital code can control up to 256 (28) different levels ofresistance to be supplied by the r-DAC. Protocols for signaling thevarying level of resistance of the r-DAC can include I2C, SMBus, SerialPeripheral Interface Bus, which further facilitate configuration of theresistive elements in the r-DAC.

In the analog core 500, the MOSFET switches 506, 508, 510, 512, 514, and516 are organized into an H-bridge. The sensing circuitry, the sensingresistor 520, senses the current flowing through the motor and theH-bridge. When the current is driven to the sensing resistor 520, afeedback voltage is generated. The feedback voltage is applied to thenegative terminal of the operational amplifier 502.

The operational amplifier 502 compares the feedback voltage to areference voltage, which is applied to the positive terminal of theoperational amplifier. A digital code representative of the referencevoltage is applied to a resistive digital-to-analog converter (r-DAC),and the output of the r-DAC is applied as the reference voltage to thepositive terminal of the operational amplifier 502.

The operational amplifier 502 generates an analog voltage that isproportional to the error between the reference voltage and the feedbackvoltage. As time passes, over a number of clock cycles, the operationalamplifier and the PWM/linear control driver 504 will influence thecurrent provided to the motor so that the current provided (Iout) isproperly regulated.

The analog core 500, described in the foregoing, can be implemented in asystem that operates a VCM in both a forward direction and a reversedirection. Further, the analog core 500 can be implemented in a systemthat drives the VCM in both a linear mode and a PWM mode.

Analog core 500 has several advantages. First, analog core 500 can bereused when the VCM operates in each of: a forward direction in a linearmode; a reverse direction in a linear mode; a forward direction in a PWMmode; and a reverse direction in a PWM mode. By maintaining the samecore analog architecture in each of these operations, analog core 500minimizes the output current error variation between the modes. Byreusing the same components, analog core 500 further minimizes theswitching times between the modes.

Analog core 500 is further advantageous in that there are no glitches inthe linear mode when the code changes. The code input to the r-DAC inanalog core 500 occurs at the positive input terminal to the operationalamplifier. By doing so, the code changes do not affect the transitionsbetween the modes. When the r-DAC is instead located within the currentvarying section of the feedback circuit, as provided with analog core600 and analog core 700, a change in the r-DAC code can produce avoltage glitch that affects the input at the negative terminal of theoperational amplifier. The operational amplifier's transfer response,based on this voltage glitch, could result in an unintended change inthe current output used to drive the motor.

FIG. 6 depicts a feedback control system having an analog core 600 and abi-directional driver 604 having a PWM mode and a linear mode.

Analog core 600 includes analog circuit components in place of thesensing circuitry described in foregoing FIGS. 1 to 4. Analog core 600capitalizes on the reuse of the sensing circuitry to reduce DC errorbetween the linear mode and the PWM mode. Analog core 600 can include:

-   -   an operational amplifier 602;    -   a set of MOSFET switches (606, 608, 610, 612, 614, and 616); and    -   sensing circuitry.

Sensing circuitry is, in analog core 600, an r-DAC (or digitalpotentiometer) 620. In some embodiments, the r-DAC includes a resistorladder integrated circuit. In other embodiments, the r-DAC includes adigital to analog converter. r-DAC 620 accepts, as an input, a digitalcode.

The digital code provides a number of bits as an instruction to ther-DAC. The number of bits characterizes, within the instruction, thedegree to which resistance should be varied in the r-DAC. For example,an 8-bit digital code can control up to 256 (28) different levels ofresistance to be supplied by the r-DAC. Protocols for signaling thevarying level of resistance of the r-DAC can include I2C, SMBus, SerialPeripheral Interface Bus, which further facilitate configuration of theresistive elements in the r-DAC.

A voltage, or a set of voltages, sensed at the r-DAC of the analog core600 can further be used to pinpoint the errors in the gain of thetransfer function of the feedback control loop. To correct these gainerrors, a signal from the r-DAC 620 can be sent for external processing.The gain error can be categorized by the external processor, and thereference voltage provided to the input terminal of the operationalamplifier 602 can be manipulated accordingly to correct for the gainerror.

Analog core 600 has several advantages. First, analog core 600 can bereused when the VCM operates in each of: a forward direction in a linearmode; a reverse direction in a linear mode; a forward direction in a PWMmode; and a reverse direction in a PWM mode. By maintaining the samecore analog architecture in each of these operations, analog core 600minimizes the output current error between the modes. By reusing thesame components, analog core 600 further minimizes the switching timesbetween the modes.

Analog core 600 is further advantageous in that any amplifier offset,inherent to the operational amplifier, does not affect the linearresponse of the feedback circuit. For example, analog core 500translates amplifier offset into an offset error in the regulated outputcurrent. Analog core 600 does not include offset error because the codeinput to the r-DAC and the modification of the current occurs in thefeedback loop, and not at the reference terminals of the operationalamplifier. Accordingly, amplifier offset does not affect the transferfunction representative of the functionality of the feedback circuit. Byinstead placing the r-DAC in feedback loop, any offset error is insteadtranslated into gain error. Gain error can be easily resolved bytrimming, or by adjusting the reference voltage at the input terminal ofthe operational amplifier.

FIG. 7 depicts a feedback control system having an analog core 700 and abi-directional driver having a PWM mode and a linear mode.

Analog core 700 includes analog circuit components in place of thesensing circuitry described in foregoing FIGS. 1 to 4. Analog core 700capitalizes on the reuse of the sensing circuitry to reduce DC errorbetween the linear mode and the PWM mode.

Analog core 700 can include:

-   -   an operational amplifier 702;    -   a set of MOSFET switches (706, 708, 710, 712, 714, and 716); and    -   sensing circuitry.

Sensing circuitry is, in analog core 700, two r-DACs 720 and 722, andswitches 714 and 716. In some embodiments, at least one of the r-DACsincludes a resistor ladder integrated circuit. In other embodiments, atleast one of the r-DACs includes a digital to analog converter. r-DACs720 and 722 each accept, as an input, a digital code. In someembodiments, the digital code provided to each of r-DAC 720 and r-DAC722 is the same digital code.

As described in the foregoing, the digital code provides a number ofbits as an instruction to the r-DAC. The number of bits characterizes,as the instruction, the degree to which resistance should be varied inthe r-DAC. For example, an 8-bit digital code can control up to 256 (28)different levels of resistance to be supplied by the r-DAC. Protocolsfor signaling the varying level of resistance of the r-DAC, can includeI2C, SM Bus, Serial Peripheral Interface Bus, which further facilitateconfiguration of the resistive elements in the r-DAC.

r-DACs 720 and 722 are each connected to a different one of the currentpaths between the switches. When the feedback system is in lineardriving mode, r-DAC 720 is connected to the path in which switch 708acts as a current source and r-DAC 722 is connected to the path in whichswitch 706 acts as a current source. When the feedback system is in PWMdriving mode, r-DAC 720 is connected to the path in which current ispulsed through switch 708, and in which switches 708 and 712 act as aninverter. When the feedback system is in PWM driving mode, r-DAC 722 isconnected to the path in which current is pulsed through switch 706, andin which switches 706 and 710 act as an inverter.

When r-DAC 720 is active, switch 714 connects the feedback voltage tothe negative terminal of operational amplifier 702 and switch 716 isopen. When r-DAC 722 is active, switch 716 connects the feedback voltageto the negative terminal of operational amplifier 702 and switch 714 isopen. Switches 714 and 716 can be configured in various ways known tothose of ordinary skill in the art. Together, switches 714 and 716 canin some embodiments be a single pole double throw switch or a singlepole changeover switch. Separately, switches 714 and 716 can in someembodiments each be configured as a single pole single throw switch.

A voltage, or a set of voltages, sensed at the respective r-DAC of theanalog core 700 can further be used to pinpoint the errors in the gainof the transfer function of the feedback control loop. To correct thesegain errors, a signal from one of the r-DAC 720 and the r-DAC 722 can besent for external processing. The gain error can be categorized by theexternal processor, and the reference voltage provided to the inputterminal of the operational amplifier 702 can be manipulated accordinglyto correct for the gain error.

Analog core 700 has several advantages. First, analog core 700 can bereused when the VCM operates in each of: a forward direction in a linearmode; a reverse direction in a linear mode; a forward direction in a PWMmode; and a reverse direction in a PWM mode. By maintaining the samecore analog architecture in each of these operations, analog core 700minimizes the output current error between the modes. By reusing thesame components, analog core 700 further minimizes the switching timesbetween the modes.

Analog core 700 is further advantageous in that any amplifier offset,inherent to the operational amplifier, does not affect the linearresponse of the feedback circuit. For example, analog core 500translates amplifier offset into an offset error in the regulated outputcurrent. Analog core 700 does not include offset error because the codeinput to the r-DACs and the modification of the current occurs in thefeedback loop, and not at the reference terminals of the operationalamplifier. Accordingly, amplifier offset does not affect the transferfunction representative of the functionality of the feedback circuit. Byinstead placing the r-DAC in feedback loop, any offset is translatedinto gain error. Gain error can be easily resolved by trimming, or byadjusting the reference voltage at the input terminal of the operationalamplifier.

In PWM mode, analog core 700 provides more accurate current sensing.This is because all of the current flowing through the motor is sensedby the appropriate r-DAC. Analog core 700 cures sensitivity issuesinherent to the analog core 600. In analog core 600, a fraction of thecurrent flowing through the motor circulates through a forward biaseddiode of an OFF device of the H-bridge in PWM mode. In both analog core600 and analog core 700, the assumption is that, at the active r-DAC,all of the current flowing through the motor is sensed and convertedinto a voltage signal. In analog core 600, this assumption is not asaccurate during PWM mode. In PWM mode, parasitic diodes consume aportion of the current that flows through the motor. Current consumptionby parasitic diodes is inherent to power switches, such as MOSFETs,which can collect and consume current. Accordingly, by implementing aset of low voltage switches in analog core 700, the current sensed andused for feedback control is more accurate.

Of the three analog cores disclosed, analog core 700 further providesthe lowest number of stacked devices. By reducing the number of stackeddevices, the consumption of power and voltage inherent to each of thedevices is minimized.

FIG. 8A depicts an embodiment of a feedback control system 800 includinga bi-directional driver that is operating in a PWM mode. In a feedbackcontrol system 800 for a VCM with a bi-directional driver that isoperating in a PWM mode, the feedback control system includes:

-   -   an operational amplifier 802;    -   a PWM/linear control driver 804;    -   a set of MOSFET switches (806, 808, 810, and 812);    -   a motor 818;    -   r-DAC 820 and r-DAC 822; and    -   voltage switches 814 & 816.

During the PWM mode, the voltage output from the PWM/linear controldriver 804 is applied directly to one switch from the first group ofMOSFET switches, which is one of switch 806 and 808. The PWM/linearcontrol driver 804 further activates one switch, which is one of switch810 and switch 812, from the second group of MOSFET switches such thatan inverter is generated. The current is driven by the combination ofthe switches through the motor 818. PWM/linear control driver 804further provides a switch control signal 832 to the voltage switches 814and 816.

One of r-DAC 820 and r-DAC 822 is used as a circuit component thattranslates the amount of current flow through the motor 418 into afeedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 802 via a voltage switch 814 or816. The operational amplifier 802 compares the feedback voltage at thenegative terminal to a reference voltage at the positive terminal andgenerates a voltage representative of the difference, or error, betweenthe reference voltage and the feedback voltage. The error is then usedby PWM/linear control driver 804 to drive the motor accordingly.

FIG. 8B depicts an illustration of the configuration of a bi-directionaldriver control 804 that is operating in a PWM mode.

For the feedback control system 800, FIG. 8B depicts the signalsprovided as outputs from the PWM/linear control 804. As the driver is ina PWM mode, the error signal from operational amplifier 802 is bufferedand applied to the negative terminal of another operational amplifier(e.g., operational amplifier 212 in FIG. 2). A ramp signal is applied tothe positive terminal of the operational amplifier. The output ofoperational amplifier, which is a square wave, is supplied to a PWMdigital control. The PWM digital control applies the output, via one of824 and 826, to one of switches 806 and 808. To activate only one switchfrom the first group of MOSFETs, the other output is turned OFF (e.g., aselection of 824 for the pulsed signal results in 826 having a 0 or OFFsignal). Provided that the feedback control system is in PWM mode, theinverse of the square wave is driven onto one of output 828 and 830 todrive a respective switch 810 and 812 from the second group of MOSFETs.Only one switch, 810 or 812, should be activated at any time.

To drive the direction of the motor 818, switch control 832 recognizes,based on the selected MOSFET switch from the first group of MOSFETs,whether the motor is being operated in a forward direction or a reversedirection. Accordingly, switch control 832 provides a signal that closesone of 814 and 816 and opens the other one of 814 and 815.

For example, when PWM digital control selects output 824 to drive 806from the first group of MOSFETs and 828 to drive 810 from the secondgroup of MOSFETs, the switch control 832 closes switch 816, which isassociated with r-DAC 822. This results in the motor being driven in theforward direction. The motor is driven in the reverse direction when PWMdigital control selects output 826 to drive 808 from the first group ofMOSFETs and 830 to drive 812 from the second group of MOSFETs. Theswitch control 832 closes switch 814, which is associated with r-DAC820.

FIG. 8C depicts an embodiment of a feedback control system 800 includinga bi-directional driver that is operating in a linear mode. In afeedback control system 800 for a VCM with a bi-directional driver thatis operating in a linear mode, the feedback control system includes:

-   -   an operational amplifier 834;    -   a PWM/linear control driver 836;    -   a set of MOSFET switches (838, 840, 842, and 844);    -   a motor 850;    -   r-DAC 852 and r-DAC 854; and    -   voltage switches 846 & 848.

During the linear mode, the voltage output from the PWM/linear controldriver 836 is applied directly to one switch from the first group ofMOSFET switches, which is one of switch 838 and 840. The PWM/linearcontrol driver 836 in linear mode does not activate either switch 842 orswitch 844 from the second group of MOSFET switches. The current isdriven by the selected switch from the first group of MOSFET switchesthrough the motor 850. PWM/linear control driver 836 further provides aswitch control signal 864 to the voltage switches 846 and 848.

One of r-DAC 8252 and r-DAC 854 is used as a circuit component thattranslates the amount of current flow through the motor 450 into afeedback voltage.

The feedback voltage is then provided as an input to the negativeterminal of the operational amplifier 834 via a voltage switch 846 or848. The operational amplifier 834 compares the feedback voltage at thenegative terminal to a reference voltage at the positive terminal andgenerates a voltage representative of the difference, or error, betweenthe reference voltage and the feedback voltage. The error is then usedby PWM/linear control 836 to drive the motor accordingly.

FIG. 8D depicts an illustration of the configuration of a bi-directionalPWM/linear control driver 836 that is operating in a linear mode.

For the feedback control system 800, FIG. 8D depicts the signalsprovided as outputs from the PWM/linear control driver 836. As thedriver is in a linear mode, the error signal from operational amplifier834 is buffered and provided directly and continuously through thePWM/linear control driver, over one of output 856 and 858, to one ofswitches 838 and 840 from the first group of MOSFETs. To activate onlyone switch from the first group of MOSFETs, the other output is turnedOFF (e.g., a selection of 856 for the pulsed signal results in 858having a 0 or OFF signal). Provided that the feedback control system isin linear mode, both of the outputs associated with the second group ofMOSFETs are OFF (e.g., 860 and 862).

To drive the direction of the motor 850, switch control 864 recognizes,based on the selected MOSFET switch from the first group of MOSFETs,whether the motor is being operated in a forward direction or a reversedirection. Accordingly, switch control 832 provides a signal that closesone of 846 and 848 and opens the other one of 846 and 848.

For example, when the linear buffered signals are provided to output 856to drive 838 from the first group of MOSFETs and 860 to drive 842 fromthe second group of MOSFETs, the switch control 832 closes switch 848,which is associated with r-DAC 854. This results in the motor beingdriven in the forward direction. The motor is driven in the reversedirection when output 858 drives 840 from the first group of MOSFETs and862 to drive 844 from the second group of MOSFETs. The switch control832 closes switch 846, which is associated with r-DAC 852.

In the embodiments described above in connection with FIGS. 5 to 7, theanalog core is described as including the switches that are used tocontrol the motor. In a further embodiment, the analog core may includethe sensing circuitry and the operational amplifiers 502, 602, 702, butnot the switches. The feedback control system may include two sets ofswitches; a first set for use with the PWM modes and a second set foruse with the linear mode. In this case, the benefits improved switchingtimes and reduced output error are still realised as a result of thefeedback path being shared between modes.

FIG. 9 depicts an illustration of the effect of an offset errorassociated with the analog core 500 on the VCM PWM/linear drivertransfer function. The DAC code, which is implemented to control thevoltage provided at the input reference terminal of the operationalamplifier, is provided as a variable along the x-axis of FIG. 9. Thecurrent output, which is driven onto the motor, is provided as avariable along the y-axis of FIG. 9. Negative DAC code values correlatewith negative current values driven onto the motor. Positive DAC codevalues correlate with positive current values driven onto the motor. Asdescribed in the foregoing, when the current output (Iout) is negative,the motor is driven in the reverse direction. When Iout is positive, themotor is driven in the forward direction. Therefore, when Iout is atzero, the motor is in transition from one of a reverse direction to aforward direction or a forward direction to a reverse direction.

902 (including 902A and 902B) and 904 (including 904A and 904B) are eachassociated with one of the polarities of the offset generated by theoperational amplifier. In the example shown, the operational amplifieroffset translates into an offset voltage of +/−2 mV.

In a first case, 902 indicates how the offset voltage error results in alinear inconsistency with the Iout centered immediately around the zerocurrent transition. For example, a DAC code of −2 (in the 902A region)is associated with a negative Iout value that is substantially lowerthan the positive Iout value that is associated with a DAC code of 2 (inthe 902B region). The sudden jump in Iout values centered around thezero region afflicts the transfer function. In the case demonstrated by902, the motor cannot be regulated precisely at very low current valuesbecause regulation can only be achieved at higher and lower currentlevels. With respect to 902, the accuracy of the current measurementsproximate to the zero current region is low.

In a second case, 904 indicates, for the opposite polarity of offsetvoltage relative to 902, how the offset voltage error results in linearinconsistency with the DAC codes centered immediately around the zerocurrent transition. For example, a DAC code of −2 (in the 904A region)is associated with a 0 mA current value. Similarly, a DAC code of +2 (inthe 904B region) is associated with a 0 mA current value. The plateauregion, in which a substantial number of DAC codes are each associatedwith a 0 mA current value, afflicts the transfer function. In the casedemonstrated by 904, the sensitivity of the current measurementsproximate to the current region is non-existent. No current is suppliedto the motor for a range of DAC codes centered around the zero currentregion.

FIG. 10 depicts an illustration of the effect of a gain error associatedwith the analog core 600 and analog core 700 on the VCM PWM/lineardriver transfer function. For each of the analog core 600 and the analogcore 700, the DAC code, which is implemented to control the current flowreturning to the operational amplifier from the power region of thecircuit, is provided as a variable along the x-axis of FIG. 10. Thecurrent output, which is driven onto the motor, is provided as avariable along the y-axis of FIG. 10 (in mA). Negative DAC code valuescorrelate with negative current values driven onto the motor. PositiveDAC code values correlate with the positive current values driven ontothe motor. As described in the foregoing, when the current output (Iout)is negative, the motor is driven in the reverse direction. When Iout ispositive, the motor is driven in the forward direction. Therefore, whenIout is at zero, the motor is in transition from one of a reversedirection to a forward direction or a forward direction to a reversedirection.

The plurality of lines having different variations in Iout are providedfor different test cases and indicate that a given code can have a rangein Iout extending from a minimum Iout to a maximum Iout. Theunpredictability associated with the slopes is attributed to the gainerror. However, the transfer function for a feedback circuit having sucha gain error does not introduce the issues described in the foregoingwith reference to FIG. 9. FIG. 10 depicts a full range of currents,without gaps, that can be used to drive the VCM. Similarly, each codeprovided to the r-DACs results in a different current output.Accordingly, the relocation of the r-DAC to the placement associatedwith analog cores 600 and 700 increases accuracy and sensitivity.

Any issues associated with the gain error can be corrected by adjustingthe reference voltage at the input terminal to the operational amplifierin the feedback loop accordingly.

In other embodiments, the analog core can include other similar circuitelements to facilitate reuse of the analog core in VCM systems thatoperate in: a forward linear mode, a reverse linear mode, a forward PWMmode, and a reverse PWM mode.

Additionally, any feature of the feedback control system, analog core,and methods of using the feedback control system described herein canoptionally be used in any other embodiment of the feedback controlsystem and methods of using the feedback control system. Also,embodiments of the system and methods of using the feedback controlsystem can optionally include any subset or ordering of the features ofthe feedback control system and methods of using the feedback controlsystem described herein.

What is claimed is:
 1. A feedback control system, comprising: an analogcore; a control driver; and an electromagnetic load of a voice coilmotor (VCM); wherein the analog core is arranged to provide feedbackfrom the electromagnetic load to the control driver in order to regulatea current consumption of the VCM; the control driver is arranged toreceive, from the analog core, an error voltage corresponding to anerror in a current applied to the electromagnetic load; and the controldriver is further arranged to control the current applied to theelectromagnetic load based on the error voltage.
 2. The system of claim1, wherein the analog core is further arranged to drive theelectromagnetic load.
 3. The system of claim 2, wherein the controldriver is further arranged to control the current applied to theelectromagnetic load using the analog core.
 4. The system of claim 3,wherein the control driver is further arranged to control the currentapplied to the electromagnetic load using a control voltage.
 5. Thesystem of claim 1, wherein the control driver is arranged to operate ina linear mode and a pulse width modulation mode.
 6. The system of claim1, wherein the control driver is arranged to operate the VCM in aforward direction and in a reverse direction.
 7. The system of claim 1,wherein the analog core includes sensing circuitry arranged to generatea feedback voltage based on a current flowing through theelectromagnetic load.
 8. The system of claim 7, wherein the analog corefurther comprises a comparator, arranged to compare the feedback voltageto a reference voltage and to generate the error voltage.
 9. The systemof claim 7, wherein the sensing circuitry includes a current sensingresistor coupled to the electromagnetic load.
 10. The system of claim 7,wherein the sensing circuitry includes at least one resistivedigital-to-analog converter coupled to the electromagnetic load.
 11. Thesystem of claim 1, wherein the analog core comprises a plurality ofswitches, arranged to drive the electromagnetic load.
 12. The system ofclaim 11, wherein the plurality of switches are a plurality of MOSFETs.13. The system of claim 12, wherein the plurality of switches arearranged as an H-bridge.
 14. The system of claim 1, wherein the systemis operated in a closed loop.
 15. A controller for a voice coil motor(VCM) in which the controller is arranged to operate the voice coilmotor bidirectionally in linear and pulse width modulation modes.
 16. Amethod of controlling a current applied to an electromagnetic load of avoice coil motor (VCM), comprising: driving an electromagnetic load of avoice coil motor (VCM); receiving from an analog core, at a controldriver, an error voltage corresponding to an error in the currentapplied to the electromagnetic load; controlling, using the controldriver, the current applied to the electromagnetic load based on theerror voltage.
 17. The method of claim 16, further comprisinggenerating, using a sensing circuit, a feedback voltage based on acurrent flowing through the electromagnetic load, wherein the sensingcircuit is part of the analog core.
 18. The method of claim 17, furthercomprising: comparing, using a comparator, the feedback voltage to areference voltage and to generate the error voltage, wherein thecomparator is part of the analog core.
 19. The method of claim 17,wherein the sensing circuit includes a current sensing resistor, coupledto the electromagnetic load, and wherein the step of generating afeedback voltage is performed using current sensing.
 20. The method ofclaim 17, wherein the sensing circuit includes at least one resistivedigital-to-analog converter, coupled to the electromagnetic load, andwherein the step of generating a feedback voltage is performed usingcurrent sensing.